How can I make a cone of light be more realistic?
You could use the material created for this answer https://blender.stackexchange.com/a/72010/29586 and use an image to mimic the lens of a torch such as this :



Adjusting the material variables can produce a result like the following :



Blend file attached 

To include the material in your own project, simply download the Blend file, open your own project, got to File, Append, select the 'torch' Blend file and navigate to the material ('Material'). Set the two Image nodes to your torch lens image (use the above one if you don't have anything more suitable) and adjust the various variables (the material nodes marked in Cyan) until you get the desired effect.